This application is in response to RFA 87-HD-02 and addresses the problem of prefertilization immunocontraception from the perspective of a defined mammalian sperm membrane component and its role in achieving contraception by the antigen's specific antibody interfering with sperm-ovum binding. This study will utilize a defined rabbit sperm membrane autoantigen, RSA, which has been characterized in rabbits but which is also present in mouse, rat, and human spermatozoa, to gain a better understanding of Prefertilization immunocontraception. The study is organized into two specific aims to address the immunologic aspect of preventing fertilization and to address the biochemical aspect of characterizing the analogous human antigen. There are two specific aims. 1) The rabbit sperm membrane autoantigen, RSA, which has been well characterized, including its amino acid sequence, will be produced as a fusion protein in E. coli in large (mg) quantities for use as an immunogen in female rabbits and mice. The female rabbits and mice will be actively immunized with the fusion protein and after insemination, their fertility determined. Antisera produced by the females will be used to determine if rabbit and mouse fertilization in vitro is inhibited, 2) The rabbit cDNA for the RSA molecule, when used as a probe at high stringency for RSA messenger RNA in other species indicates that an analogous molecule is present in mouse, rat and human testes. Since the long range goal of any immmnocontraceptive study is to find application in human reproduction, this aim will concentrate on the human antigen and isolate the analogous human cDNA for RSA from a human testis cDNA library. The human antigen will be characterized by sequencing the human cDNA. This will allow comparison with the rabbit molecule and the recognition of sequences in the human molecule which might later serve as targets for contraceptives. The human fusion protein will be produced in E. coli. This will allow for the production of specific antisera which can in turn be used to identify and isolate the native human antigen.